Hello forummembers ,
My biamp dream came true by bying the BAT VK1000 monoblocks.Mariage in heaven,BTW the loudspeakers are B&W 800N , ready for biamping!. |
And I also picked up a BAT VK-5 preamp to go with the VK-60 amp. |
I sold the Classe after months of trying to sell it and people not paying shortly after posting this thread. |
How did the bi-amping work out for you? |
Maybe the gain issue can be controlled with a AV preamp ?? |
The important part will be to think this through carefully. |
I have a PS Audio 5.6 that does active and passive with 2 outs. I will have to get a variable attenuator from ebay. This will get the ball rolling. I have been living with the speakers for 5 years now so I will find out if this is a good or bad thing. |
To be perfectly accurate, I should add a minor qualification to the following statement in my previous post, which does not affect my conclusions: ... visualize an ordinary single-amp arrangement. A given input voltage at a treble frequency will result in the same output voltage as would result if that input voltage were at a bass frequency. A passive biamp arrangement needs to behave similarly, or an imbalance between the treble and the bass will result. In both cases, single amp and passive biamp, a given input voltage has to result in the same output voltage regardless of frequency. In saying this, I am ignoring small voltage differences that may occur as a result of interaction between amplifier output impedance and variations of speaker impedance as a function of frequency, in the case of tube amps having low damping factor/high output impedance. Regards, -- Al |
Didn't Von Schweikert go out of business? |
Albert VonS is never wrong, right? :) |
With all due respect to Mr. Von Schweikert, he must have been having a bad day when he wrote that. He is wrong in two respects, in the case of passive biamping of a speaker that has been designed to work ok either biamped or single amped (as opposed to the unusual situation of a speaker made up of completely separate elements for the different frequency ranges, that will only work properly when separate amps are used for each element, with an active crossover ahead of them):
1)What has to be matched is gain, not sensitivity. Although several decades ago it was defined differently, sensitivity is defined in modern times as the input voltage required to drive the amp to its rated maximum power. If both amps have a sensitivity of, for example, 1 volt, but one amp puts out 500 watts in response to the 1 volt while the other puts out 100 watts, clearly there is a problem.
2)In a passive biamp arrangement with properly matched gains, a given input voltage will result in the same output voltage from both amps, as it must for proper frequency balance. Therefore (as I indicated in my previous post) if the two amps have very different power capabilities (which he suggests would be a good approach), only a small fraction of the power capability of the higher powered amp can be utilized, without clipping the lower powered amp.
If that is not clear, visualize an ordinary single-amp arrangement. A given input voltage at a treble frequency will result in the same output voltage as would result if that input voltage were at a bass frequency. A passive biamp arrangement needs to behave similarly, or an imbalance between the treble and the bass will result. In both cases, single amp and passive biamp, a given input voltage has to result in the same output voltage regardless of frequency.
And since in a passive biamp configuration there is no filtering ahead of the amps to separate high frequencies from low frequencies, the output voltage of the high frequency amp will include low frequency components that are identical in voltage to those that are present in the output voltage of the low frequency amp, and vice versa.
And it is safe to assume that the maximum output voltage that can be generated by a 60W amp will be far less than can be generated by an 800W amp. Therefore, as I indicated, most of the power capability of the 800W amp cannot be used, in a passive biamp configuration, without clipping the 60W amp.
Regards,
-- Al |
From Albert Von Schweikert:
Hello Fellow Audiophiles,
Over the past 32 years, I've used bi-amping as a method to achieve more realistic sound quality. A decent, high powered solid state amplifier will give you explosive and tight bass power, while a smaller tube amp will give you the "air" and image float you are seeking from your sound system. Here are a few tips:
1. The bass amp does not have to necessarily be expensive, but make sure it has a large transformer and power supply to ensure "tight" bass. All of our speaker designs employ 4-ohm woofer systems, with a dip down to 3.5 ohms, so make sure the amp is stable into a 4 ohm load. Power requirements depend on your room size and how loud you want to go. I suggest 200-300 watts per channel if you have a large room and want an explosive dynamic range.
2. The tube amplifier can have as little as 20 watts per channel in a small room, but in a large room, you may want to have 50-100 watts per channel to avoid clipping at high volume levels. Due to the distribution of power over the frequency range of 20Hz to 20kHz, you can use a much smaller amplifier on the midrange and tweeter module. Use the 8-ohm taps on the tube amp, but feel free to experiment - it won't hurt anything to try other taps.
3. The "secret" to achieve "killer" sound quality is to ensure that the amplifiers have exactly the same input sensitivity. The amplifier with the lowest numerical rating, i.e. 100mV is much more sensitive than an amplifier with a rating of 500mV - the higher the number, the lower the sensitivity. You'll need to reduce the higher sensitivity by using a series input resistor. This can be installed inside your amplifier, directly at the RCA female jack leading to the input stage. If this sounds a little scary, then build an adaptor to house the resistor outside the amp. If you contact Michael Percy at www.percyaudio.com, he will advise you on what you'll need to get from him. Usually, a female RCA jack, a male RCA plug, a high quality metal film resistor, some plastic sleeving, and a short piece of high quality hookup wire is all that is required. Basically, you're inserting the resistor between the "hot" connection from the female RCA jack to the male RCA plug, and then using hookup wire to connect the ground leads. The entire assembly can be only a few inches long and installed into a plastic or Teflon sleeve to prevent short circuits. This adaptor is inserted into the signal path between your preamp and the most sensitive amplifier. As you can infer from this description, the adaptor is used in between your interconnect and the input jack of the amplifier.
Michael Percy sells these parts for less than $100 for everything you'll need, and he'll also help you select the proper value of resistor to match the sensitivities. Although this simple technique may sound like a "Micky Mouse" setup to "sophisticated" engineers that design chip OP AMPS and sell electronic crossovers to the PA industry, it is a very "pure" form of passive matching that will stomp the crap out of any electronic crossover I have ever tried.
4. Brands and Models: basically, put your money into the tube amp, since even inexpensive solid state amplifiers have stiff power supplies and enough quality to drive woofers with high speed transient response, high volume levels without clipping, and tight bass. Twenty years ago, Adcom built a 200-watt amplifier for around a thousand bucks new, and half that price used. Today, there are many expensive amplifiers that sound great, but you're paying for an expensive chassis, face plate, branding (advertising), and so forth. Instead, look for an amp with a large transformer and high quality power supply.
Tube amplifier choices abound, at all price ranges. Some of the best values are from China if you are on a budget, but large American tube amps from long established companies will be a good investment, with good resale value and the ease of repairs. Don't worry about the availability of tubes, they're going to be around for another 50 years or more due to the ever-expanding market for tube amplifiers.
Happy Listening from Albert Von Schweikert
|
I picked up the Bat @ $1000 it needs some repair. That would be a good time to put V-Caps in it. So, The Classe is not selling which I was going to buy a tube amp with the funds but it looks like I will have 2 amps now. That is how I got the idea, good or bad I dunno. I will have them so why not give it a go. The Classe has been sold a few times, people that wanna buy stuff and paying for it are 2 different animals. |
Passively biamping with amplifiers having very different power capabilities creates an additional problem, besides the need to gain match and the possibility of sonic issues due to the amp's having differing sonic characters. You would not be able to utilize most of the power capability of the higher powered amp.
Your Classe amp is rated at 800 watts into the 4 ohm nominal impedance of your speakers. The BAT is rated at 60 watts into 4 ohms. In a properly gain matched passive biamp arrangement both amplifiers have to output identical voltages at any instant of time, in a given channel, corresponding to the full frequency range signal. Therefore you would not be able to raise the volume control high enough to utilize most of the power capability of the Classe amp without clipping the BAT amp, which if clipped would result in severe distortion and possibly even blown tweeters. In effect, you would be converting the 800 watt Classe into perhaps (just guessing) a 100 or 150 watt amp, depending on how much voltage the BAT amp is capable of putting out.
Using an active crossover ahead of the amps would resolve that problem, at least mostly, and would also presumably allow you to gain match. You would still be left with the possibility that sonics may be adversely affected by the different sonic characters of the two amps, particularly at frequencies that are in the crossover region, where both amps would be contributing to the sound that is heard.
I have no particular familiarity with active crossovers, but if you want to go that way models that should be looked into are made by Marchand, Bryston, and Rane.
Regards,
-- Al |
http://www.drhifi.net.au/Used%20Equipment/Classe%20CA-400/1.htm
http://www.balanced.com/products/amp/specs.O.shtml
http://www.goldpt.com/bal_amps.html |
What are some examples of active crossovers ?? I may go passive also so that may be a problem solved. |
You will need an active x-over or a pre w two outputs and a pair of variable attenuators on the signal to the amp w more gain. |
